Fuel Injection Made Easy From FAST

Converting an engine originally equipped with a carburetor to electronic fuel injection (EFI) is nothing new; though every year it seems as if interest in taking the EFI plunge gains momentum. OEM vehicles of the past two decades have firmly engrained the advantages of fuel injection to all but the most diehard enthusiasts. Far be it from us to suggest taking a show-bred Corvette and altering it in such a way. however, if serious road time is more important than originality in your Vette escapades, retrofitting to EFI is a modification worth considering. Late-model performance cars, such as the C5 and C6, provide all the evidence necessary to show the attributes of injection, including flawless drivability and remarkable reliability. Wouldn't it be nice to take some of that technology and apply it to an earlier carbureted Corvette?

For the vast majority of enthusiasts, the thought of running a custom aftermarket EFI system is filled with trepidation. Sure, it seems to work great on modern cars, but just what is involved in setting up an older engine to work with this modern technology? At first glance it might seem pretty complex, with items such as the wiring, sensors, the control box, and so on. In comparison to that old Quadrajet, it certainly involves more hardware and at a more sophisticated level, but breaking it down is nothing a seasoned wrench-turner couldn't handle. We sought just such a conversion to a small-block Chevrolet engine and found the changeover less daunting than anticipated, using components from FAST.

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The basic hardware change when making the move to EFI is the intake manifold, which isn't terribly surprising since we are talking induction systems here. One of the key components is the intake manifold, and there are a myriad of choices. There are purpose-built EFI manifolds available from the aftermarket, and some available with EFI bosses cast in, which need machining to accept the injectors. Manifolds originally intended for carbureted applications can also be readily adapted, as evidenced by our own Edelbrock Victor Jr. Note the injector bungs TIG welded to the runners on this intake. The universal bungs are available from FAST.

Back in the early days of EFI conversions, most efforts centered upon adapting the primitive OEM components of the time to vintage iron. Installing the hardware was simple enough, but the difficulty stemmed from gaining control of the tuning parameters. Such installations nearly always involved modifications to the factory specifications, and the control units that provided the logic to run the systems were notoriously inflexible. Times have changed, and these days companies like FAST do the work to produce components that have been designed to work together, in a wide range of potential applications. the technology is built into the system, so the end user does not need to be a fuel-system engineer. The software facilitates tuning the system to an unbelievable degree, making such installations flexible in controlling a wide range of likely combinations.

Whether you are looking to inject an older Corvette cruiser, or are looking to plant a modern, fuel-injected monster in your radically modified C3, the systems to make it happen have already been ironed-out to the nth degree.

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In an EFI system, we find a throttle body in the location normally occupied by the carburetor. The throttle body only meters the air flow into the engine, and handles none of the fuel.

Is there EFI in the future of your seasoned Vette? It's pretty hard to ignore the drivability of modern systems that continually adjust the fuel and spark to their optimal settings as you drive. Equipped with modern controls, you're practically rolling down the road with an ace tune-up man wrenching away under the hood at all times. An expertly calibrated fuel-injection system can eliminate the temperamental nature that some carbureted installations can exhibit, and make driving the pleasure it was intended to be. Everything you need is readily available from EFI specialty companies such as FAST, so what are you waiting for?

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Serving as the "brains" of an EFI system is the electronic control unit. The new FAST XFI box is a state-of-the-art aftermarket engine control system with greater flexibility and more user-friendliness than ever before. Changes to the hardware and accompanying software expanded the capabilities of the system, allowing control over the full spectrum of engine fuel and timing functions, as well as auxiliary outputs to control a variety of additional devices, including everything from torque converter lock-up to fan actuation. Multiple LED's on the FAST XFI box confirm inputs from crank, cam (if applicable), ignition trigger, and power, while a second series shows cylinder firing output.

It is important for the control unit to know the load being placed upon the engine at all times. The manifold air pressure (MAP) sensor provides this information. Essentially, this sensor reads manifold vacuum, with lower vacuum equating to higher load. Hooking up the MAP sensor is as simple as running a vacuum line from the manifold or a point below the throttle plates on the throttle body to the MAP sensor, and then plugging in the harness connection marked MAP.

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EFI requires a different fuel system than that used in a carbureted application because of the much higher fuel pressure. Typically, injectors are rated for flow at 45 psi. That is the normal pressure setting used with a FAST system and is best set using a bypass regulator. A pump that can provide sufficient pressure is a must, and it also must flow the required volume for the power output of the engine. FAST's tech help can provide sizing information on both the fuel-system components and the injectors themselves. Size and capacity has to match the application, based on anticipated power output.

Carburetion Vs. InjectionConverting to EFI is not a decision that should be based upon looking for outrageous power gains, but rather for the best drivability and efficiency gains possible. The naked truth is, given exactly the same components, the power of a perfectly tuned carburetor will be virtually identical to an EFI system. One of the key differences is an EFI system is "smart" and once programmed correctly, will always be in perfect tune, no matter how the operating conditions of temperature and air density changes. We installed a Demon four-barrel carburetor to the tuned EFI system on the dyno just to compare the wide-open-throttle output. Not surprisingly, with the combination otherwise identical, the power curve was virtually unchanged, with the EFI gaining a modest advantage in low-speed torque. However, by taking advantage of the intake manifold design flexibility available when running EFI, the power characteristics can be changed significantly. Modern plenum ram manifolds of the type used on the LS-family of engines are a good example. This design takes positive advantage of inertia ram tuning for a healthy boost in torque, but such a manifold layout would be impossible in a carbureted application.

While an EFI system can be tuned to a fine set of parameters at the keyboard of a computer, a carburetor is a mechanical device with fuel curve adjustments primarily handled by changing jets, altering the orifice restricting fuel flow. Tuned for a perfect air/fuel ratio, output is about equivalent when considering full-throttle horsepower and torque, if all else in the engine remains unchanged.

A lot of reasons can be found as to why engines perform one way or the other as well as improve and its attributed to the EFI. Here is a primer on the modern miracle of Electronic Fuel Injection. - GM High-Tech Performance Magazine » Read More